This may turn into more of a science project than you want.
I’ve seen car guys powder coat plastic parts but it was NOT with the standard charge + spray + bake process. Since the plastic will not hold a charge they heat the plastic part up in an oven or with a heat gun, spray on the powder, and then use the heat gun to bake on the powder.
For one off parts it’s fine, but it is not an easily repeated mass production process and will not work well if you are trying to do a metal part at the same time.
I’d consider coating your aluminum part, color matching your plastic, painting your plastic, or embracing a color break in the materials.